General Information
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| Illustration 1 | g00328150 |
Air Inlet And Exhaust System Schematic (1) Air inlet. (2) Turbocharger. (3) Air inlet choke. (4) Aftercooler. (5) Main gas supply. (6) Cylinder head inlet port. (7) Precombustion chamber gas supply. (8) Precombustion chamber. (9) Spark plug. (10) Exhaust valve. (11) Exhaust. (12) Inlet valve. (13) Exhaust bypass control valve. | |
The components of the air inlet and exhaust system control the quality and the amount of air that is available for combustion. The inlet manifold (air plenum) is a passage inside the cylinder block. This passage connects the aftercooler to the inlet ports in the cylinder head. The camshaft controls the movement of the valve system components.
Air Inlet And Exhaust System Components
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| Illustration 2 | g00328151 |
Air Inlet And Exhaust System (1) Exhaust manifold. (2) Aftercooler. (3) Air choke. (4) Exhaust outlet. (5) Engine cylinder. (6) Air inlet. (7) Turbocharger compressor wheel. (8) Turbocharger turbine wheel. (9) Exhaust bypass valve. | |
Clean inlet air from the air cleaners is pulled through air inlet (6) into the turbocharger compressor by the turbocharger compressor wheel (7) . The rotation of the turbocharger compressor wheel causes the air to compress. The rotation of the turbocharger compressor wheel then forces the air through an elbow to the aftercooler (2) . The aftercooler lowers the temperature of the compressed air before the air enters the air plenum. This cooled and compressed air fills the air plenum. The air fills the inlet chambers in the cylinder heads. Air flow from the inlet chamber into the cylinder is controlled by the inlet valves. Fuel (gas) flow into the cylinder is controlled by the gas admission valve.
There are five valves in each cylinder head. There is one gas admission valve (refer to System Operation, "Fuel System" ), two inlet valves and two exhaust valves for each cylinder. Make reference to "Valve System Components". The inlet valves and the gas admission valve, open when the piston moves down on the intake stroke.
The camshaft controls the opening of the valves. The cooled, compressed air is pulled into the cylinder from the inlet chamber along with the gas that is supplied through the gas admission valve. The gas admission valves and the inlet valves close and the piston starts to move up on the compression stroke. When the piston is near the top of the compression stroke, the rich air fuel mix in the precombustion chamber has been leaned to a combustible mix and is ignited by the spark plug. The force of the combustion pushes the piston down on the power stroke. When the piston moves up again the piston is on the exhaust stroke. The exhaust valves open and the exhaust gases are pushed through the exhaust port into the exhaust manifold (1) . After the piston makes the exhaust stroke, the exhaust valves close. The cycle (intake, compression, power, exhaust) starts again.
Exhaust gases from the exhaust manifold cause the turbocharger turbine wheel (8) to turn. The turbine wheel is connected to the shaft that drives the compressor wheel. Depending on the speed and the load requirements of the engine, exhaust gases are directed either through the exhaust outlet to the turbocharger or through the exhaust bypass valve.
An actuator controls the position of the exhaust bypass (wastegate) valve (9) . The wastegate actuator provides the desired inlet manifold air pressure. This is based on a command signal that the actuator receives from the ECM. The ECM determines the command signal. The command signal is based on the difference between the actual air/fuel ratio (or average combustion burn time) and the desired air/fuel ratio (desired combustion burn time).
The position of air choke (3) is controlled by an actuator. The choke actuator provides the desired inlet manifold air pressure during part load operation. This is based on a command signal that actuator receives from the ECM. The ECM determines the command signal based on the engine speed (rpm) and the engine load (calculated value based on pressures and temperatures that are measured on the engine).
Aftercooler
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| Illustration 3 | g00485390 |
Air Inlet And Exhaust System Components (1) Coolant outlet connection. (2) Coolant inlet connection. | |
The aftercooler is located on the left rear side of the engine at the rear opening of the plenum. The aftercooler has a coolant charged core assembly. Coolant from the water pump on the left side of the engine flows through coolant inlet connection (2) . Coolant circulates through the core assemblies. The coolant then exits the aftercooler through the coolant outlet connection (1) .
Inlet air from the compressor side of the turbocharger flows into the aftercooler housing. The inlet air passes the fins in the core assemblies. The aftercooler core lowers the temperature of the air. The cooler air is directed into the air plenum. The cooler air is directed up and through the inlet ports of the cylinder heads.
Lowering the temperature of the inlet air will increase the density of the air (per volume). The increased air density will result in more efficient combustion and in lower fuel consumption.
Turbochargers
The turbine side of the turbocharger is connected to the exhaust manifold. The compressor side of the turbocharger is connected to the aftercooler. Both the turbine (exhaust) and compressor (inlet) are connected to the same shaft and rotate together.
The exhaust gases go into the turbocharger through the exhaust inlet adapter. The exhaust gases push the blades of the turbine wheel. This causes the turbine wheel and compressor wheel to turn.
Clean air from the air cleaner is pulled through the compressor housing air inlet by the rotation of the compressor wheel. The action of the compressor wheel blades causes a compression of the inlet air. This compression gives the engine more power because it makes it possible for the engine to burn additional fuel with greater efficiency.
The bearings in the turbocharger use engine oil under pressure for lubrication. The oil comes in through the oil inlet. The oil goes through the passages in the center section for lubrication of the bearings. The oil goes out of the oil outlet. The oil returns to the oil pan.
The turbocharger turbine (exhaust) section and the center (bearings) sections are enclosed in a water cooled housing.
Exhaust Bypass
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| Illustration 4 | g00488125 |
Exhaust Bypass Valve (1) Adjustable linkage. (2) Wastegate. (3) Actuator. | |
The exhaust bypass is operated by one of the three actuators that are used to control the air/fuel ratio of the engine. One actuator controls fuel flow. The other two work together in order to control the amount of air supplied to the engine throughout the entire speed and the load range. The exhaust bypass actuator (3) is located on the left rear of the engine, next to the gas inlet actuator. The exhaust bypass actuator receives an electronic command signal from the Engine Control Module. The signal mechanically changes the position of the exhaust bypass valve in order to give the optimum air/fuel ratio for the operating conditions. The position of the valve is changed through an adjustable linkage (1) .
The position of the plate for the exhaust bypass valve is represented by the slot that is cut into the end of the shaft. When the Engine Control Module requests a leaner air/fuel ratio, the actuator will move the adjustable linkage (1) in order to close the exhaust bypass valve. This will allow more of the exhaust gases to go into the turbocharger. The additional exhaust gases will increase the rpm of the turbocharger. The increase in the rpm will cause more inlet air to be drawn into the engine. The inlet air will be compressed and the inlet air will be sent to the cylinders. When the Engine Control Module requests a richer air/fuel ratio, the actuator will open the exhaust bypass valve. The opening of the exhaust bypass valve will allow a portion of the exhaust gases to go out of the exhaust adapter instead of through the turbocharger. Less of the inlet air is compressed and sent to the cylinders.
The electronic command signal that is sent to the actuator is a percent pulse width modulated (PWM) signal. For diagnostic purposes, the actuator sends a VDC position feedback signal back to the ECM.
Inlet Air Choke
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| Illustration 5 | g00488128 |
Inlet Air Choke (1) Actuator. (2) Adjustable linkage. (3) Choke plate. (4) Turbocharger outlet. | |
The air (choke) actuator (1) is one of three actuators that is used to control the air/fuel ratio of the engine. One actuator controls fuel flow. The other two actuators work together in order to control the amount of air that is supplied to the engine throughout the entire speed and load range. The actuator is located on the left rear of the engine. The actuator receives an electronic signal from the Engine Control Module. The actuator mechanically changes the position of the air choke plate (3) via an actuator lever and adjustable rod (2) .
The position of the plate is represented by the slot that is cut into the end of the shaft. The movement of the choke plate controls the air flow from the turbocharger outlet, through the inlet air choke. The air will then flow through the aftercooler into the cylinder block air plenum, and then into the cylinder head. Fuel is introduced to the air in the cylinder head by the gas admission valve.
At full load and full speed, the actuators will operate the engine with the air choke in the fully open position. This in order to reduce the restriction to the air flow and improve the engine operating efficiency. The ECM will use the exhaust bypass system in order to control the air/fuel ratio of the engine. As engine load decreases, the inlet air choke begins to restrict air flow into the air plenum of the cylinder block. This is done in order to maintain a sufficiently rich mixture for good combustion at lighter engine loads. This combination of control (exhaust bypass/inlet air choke) provides for the increased improvement in fuel consumption at part load conditions, while also allowing complete control at full load conditions.
Exhaust Manifold
The exhaust manifold is a dry design that utilizes a thermal blanket for reduced radiant heat rejection. A dry manifold is possible because of the inherently low exhaust manifold temperatures of lean burn combustion. Engine performance is enhanced, especially for constant torque and variable speed industrial applications, by retaining the exhaust system energy in order to drive the turbocharger.
Valve System Components
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| Illustration 6 | g00328157 |
Valve System Components (1) Rocker arm. (2) Gas admission valve rocker arm linkage. (3) Bridge. (4) Gas admission valve. (5) Pushrod. (6) Lifter. | |
The valve system components control the flow of inlet air, fuel and exhaust gases into the cylinders and out of the cylinders during engine operation.
The crankshaft gear drives the camshaft gears through idler gears. The camshafts must be timed to the crankshaft in order to get the correct relation between the piston and the valve movement.
The camshaft has three camshaft lobes for each of the cylinders. One lobe operates the bridge that moves the two inlet valves. One lobe operates the bridge that moves the two exhaust valves. The center lobe operates the single gas admission valve.
As the camshaft turns, the lobes of the camshaft cause lifters (6) to go up and down. The movement of the lifters will cause the pushrods (5) to move the rocker arms (1) . Movement of the rocker arms will cause the bridges (3) to move up and down on dowels in the cylinder head. This movement will operate the valves. The bridges will allow one rocker arm to open or close the two valves (inlet or exhaust) at the same time. A separate lifter and gas admission valve rocker arm linkage (2) are working together (no bridge) in order to operate the gas admission valve (4) . There is one gas admission valve, two inlet valves and two exhaust valves for each cylinder.
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| Illustration 7 | g00328159 |
Valve System Components (7) Rotocoil. (8) Valve spring. | |
Rotocoils (7) cause the valves (gas admission valve, inlet valve and exhaust valve) to turn while the engine is running. The rotation of the valves keeps the deposit of carbon on the valves to a minimum. The rotation of the valves gives the valves longer service life.
Valve springs (8) cause the valves to close when the lifters move down.
Hydraulic Actuator System (Hydrax)
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| Illustration 8 | g00488171 |
Hydraulic Actuator System (1) Fuel actuator. (2) Position feedback sensor. (3) Exhaust bypass actuator. (4) Pressure relief valve. (5) Accumulator. (6) Hydraulic pump. (7) Hydraulic tank. (8) Hydraulic oil filter. (9) Pressure switch. (10) Air choke actuator. (11) Check valve. | |
The Caterpillar hydraulic actuator system is used to control the fuel actuator (1) , the exhaust bypass actuator (3) and the air choke actuator (10) by using individual electronically controlled hydraulic actuators.
An engine driven hydraulic pump (6) provides the required fluid pressure. The pump is gear driven from the engine front gear train. The pump is mounted behind the engine oil pump. The pump will provide hydraulic fluid at approximately 8 gpm at 1000 rpm engine speed.
A hydraulic tank (7) stores the hydraulic fluid. The hydraulic tank has a capacity of 26.5 L (7 US gal). A check valve (11) keeps the oil from draining from the system. This will allow better response characteristics.
An accumulator (5) maintains the system pressure. The accumulator maintains the system pressure for a short period of time after an engine shutdown condition is requested. This will allow the occurrence of the proper shutdown sequence. The accumulator is a nitrogen charged bottle. The accumulator is factory preset to a pressure of 1400 kPa (200 psi) .
A pressure switch (9) protects the engine in case of a hydraulic oil leak. The switch activates a warning when the system pressure reaches 1206.5 kPa (175 psi). An engine shutdown will occur if the system pressure drops below 689.5 ± 103.4 kPa (100 ± 15 psi) .
The system uses standard Caterpillar hydraulic oil and a Caterpillar hydraulic oil filter (8) . The filter should be changed yearly.
A pressure relief valve (4) is in parallel with the three actuators. The pressure relief valve is manually adjusted at rated engine speed in order to obtain a system pressure of 1722.5 kPa (250 psi). Field installation of a pressure gauge is required in order to set the system pressure. Once the system pressure is set, the pressure gauge can be removed. The pressure setting should be done once the hydraulic fluid has reached a stable operating temperature.
The three actuators receive the system pressure near the setting of 1722.5 kPa (250 psi). The actuators are electronically controlled. The actuators are monitored by the Engine Control Module.
Position feedback sensors (2) mount to the appropriate fuel shaft, exhaust bypass shaft and air choke shaft. A separate driver module box contains the individual actuator driver modules. The "driver modules" provide the interface between the engine control and the actuators.
The hydraulic actuators, the position feedback sensors and the driver modules are interchangeable. This will allow for different troubleshooting options in order to better isolate a system problem.